Well I think that if you have a strong relationship you should always trust your boyfriend, i can understand that as women we become emotional, but I understand men tend to see it as we are being insecure about ourselves, and feels like to them we are being Jealous. I was in one of these situations before myself, and responded the same way. Fortunately the guy I was with just was not a healthy person to be with.
If your boyfriend doesn't understand that he's not protecting his relationship with you by setting himself up with other girls, he better learn. It's usually the way relationships get in trouble by allowing themselves to be alone with the opposite sex. They may not intend to get involved or something to happen sexually, but it often does, and the girl might just get the wrong idea. Or maybe she has the right idea, and wants to compete with you. It's hard to say, but I've watch many women and men in action on the internet, and some times they just don't set their boundaries and the relationship ends because someone was cheating, or controlling, or manipulating.